The presently available techniques employed in Parts I and II of the program project "Nuclear Techniques in the Study of Metabolism and Bone Disease" (NIH Grant Number AM 17930-01) for assessing the status of the skeleton in vivo for both animal and man include metabolic balance studies, photon absorption densiometry and bone biopsies. These techniques are either expensive, time consuming or incapable of measuring small changes in skeletal calcium. A method which is safe, precise and repeatable for the monitoring of changes of skeletal calcium is in vivo neutron activation analysis. The objective of this supplemental proposal is to develop an in vivo neutron activation analysis facility at the Massachusetts Institute of Technology. Such a facility would be used, initially, to measure the whole body content of calcium and other elements in Rhesus monkeys with osteoporosis in Part I of the program using a Cockroft-Walton neutron generator. The "prompt" gamma ray spectrum emitted from the monkeys during neutron irradiation will be monitored with a Ge(Li) detector. The decay gamma ray spectrum from radioisotopes produced during neutron activation analysis will be monitored with a sodium iodide whole body counter specifically tailored for the monkeys. For Part II of the program, in vivo neutron activation analysis will be performed to measure the content of calcium and other elements in the hands of patients suffering from a variety of diseases such as osteoporosis and hyperparathyroidism. For these studies four 100 micron gm Cf252 neutron sources, moderated by H2O, will be the source for the hand. The decay gamma rays from radioisotopes produced during neutron activation will be monitored with a pair of large sodium iodide detectors. The proposed facility is designed to measure small changes (greater than 2 percent) in skeletal calcium in man and animals so that the program project goals can be reached.